Gray scale gaseous display

ABSTRACT

An improved gaseous display arrangement is disclosed in which a 2n level gray scale is provided by stacking n conventional gas discharge display devices separated by respective light attenuating layers, each layer attenuating the display light reaching the viewing surface by a factor of two. The display devices in the stack are addressed in common, respective bits of an n-bit gray scale codeword determining the ON-OFF character of the individual display devices. Multicolor displays are achieved by the use of different gases in the several devices or by the use of appropriate filters between the devices.

United States Patent [72] Inventor Dinh-Tuan Ngo Colts Neck, NJ. [21]Appl. No. 887,994 [22] Filed Dec. 24, 1969 [45] Patented Dec. 7, 1971[73] Assignee Bell Telephone Laboratories, incorporated Murray lllill,NJ.

[54] GRAY SCALE GASEOUS DISPLAY 15 Claims, 11 Drawing Figs.

[52] U.S.Cl 315/167, 313/112, 315/169 [51] Int. Cl 11051 37/00 [50]Field of Search 313/1095, 112; 315/167, 169, 169TV [56] References CitedUNITED STATES PATENTS 3,015,747 2/1962 Rosenberg 315/169 TV SIGNALSOURCE ADDRESS CCT.

susmmme SIGNAL souncr I CO NT ROL cmcupi e0 3,042,823 7/1962 Willard3,114,065 12/1963 Kaplan Primary Examiner-Roy Lake AssistantExaminer-Lawrence .l. Dahl Attorneys-R. J. Guenther and Kenneth B.Hamlin PATENTED DEC 7 I971 SHEET 2 BF 3 AQQQLE! FIG. 6

SIGNAL SOURCE PATENTED DEC 7197! 3,626, 241

SHEET 3 OF 3 WRITE PULSE SUSTAINING Vb SIGNAL ISIS IS CELL ADDRESS GRAYFIG. 7C SCALE SIGNALS l I I 7m DISPLAY k FIG. 70 CELL xb CURRENT 703 P IDISPLAv FIG. 75 CELL X0 1 CURRENT GRAY SCALE GASEOUS DISPLAY BACKGROUNDOF THE INVENTION This invention relates to display devices, and moreparticularly, to display devices upon which images are generated by theselective energization of individual display cells or elements.

Display devices are typically used for generating patterns ofinformation or images in a two-dimensional raster for informationdisplay media, television, radar, computer input/output terminals, andthe like. The principal types of display devices currently availableinclude cathode-ray tube presentations, which suffer from well-knowndisadvantages related to size, cost, ruggedness and power requirements.The need for a display device which would overcome these disadvantageshas been apparent for some time and considerable effort has beenexpended toward achieving such a display device.

Currently one of the areas of greatest promise appears to be gaseousdisplays of the type generating display images through the breakdowndischarge of a gas, particularly such displays utilizing pulseddischarges to breakdown a gas to lightemitting plasma. Plasma displaysare digitally addressable and have inherent memory, the lattereliminating the need for external memory storage and associatedcircuitry to regenerate the display image. However, known plasma displaydevices, as well as other gaseous discharge display devices, in view oftheir basic ON-OFF characteristic, suffer from an absence of themultilevel gray scale or variable contrast required for television andother similar display applications.

Time division multiplexing arrangements have been proposed for providingsuch displays with the required gray scale by varying the duty cycle;that is, by energizing the individual display cell elements for varyingdurations during each scanning frame. However, such known arrangementshave so far proven to be too costly and complex from a manufacturingstandpoint.

Another approach has been to array the display cells in spot clusters,selected cells or combinations thereof in a cluster being energized fordifferent desired intensities or gray. scale levels. This approach hasnot proven entirely satisfactory due principally to variousmanufacturing problems and to problems related to cell addressing andimage resolutions.

SUMMARY OF THE INVENTION It is accordingly an object of this inventiontoprovide a new and improved gaseous display arrangement having amultilevel gray scale.

More particularly, it is an object of this invention to provide a newand improved gray scale gaseous display arrangement which alleviates thedisadvantages of known arrangements.

A conventional gaseous display device, such as a plasma display device,typically comprises a coordinate array of crosspoint display cellsdefined by row and column conductors which are spaced apart by first andsecond layers of dielectric material having a layer of gaseous displaymaterial disposed therebetween. According to a feature of my invention,the above and other objects are attained in a simple and economicalmanner in an illustrative embodiment of a gray scale gaseous displayarrangement by stacking a plurality of conventional gaseous displaydevices separated by respective light-attenuating layers. Eachsuccessive light-attenuating layer in the stack attenuates the lightreaching the viewing surface by a predetermined amount, illustrativelyby a factor of two. Thus, the light reaching the viewing surface fromthe second display device level in the stack isattenuated by a factor oftwo, from the third by a factor of four, from the fourth by a factor ofeight, etc.

Accordingly, a 2" level gray scale is achieved in accordance with myinvention with a stack ofn display devices. For example, a 64-Ievel grayscale, which is more than adequate for commercial televisionapplications, is provided by an arrangement of six gaseous displaydevice levels and five light attenuating layers interleaved therewith,having a combined thickness on the order of one-tenth inch or less.

An important advantage ofagray scale gaseousdisplay arrangement inaccordance with my invention is that addressing may be effected via asingle conventional addressing circuit employed in common for alldisplay device levels, with each bit of an n-bit gray scale codeworddetermining the ON-OFF character of the respective display levels.Moreover, an arrangement according to my invention is compact andreliable, is significantly less expensive to manufacture, than knownarrangements, and provides better'resolution than arrangements usingcell clusters. In addition, my invention is particularly suited to colortelevision applications by appropriate selection of display gases or bythe use of appropriate filters between the display levels.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects andfeatures of the invention may be fully apprehended from the followingdetailed description and the accompanying drawing in which:

FIG. l-is'a diagram of an illustrative embodiment of-a gaseous displayarrangement providing a multilevel gray scale in accordance with theprinciples of my invention;

FIG. 2 shows a portion of the display embodiment of FIG. 1 in crosssection;

FIG. 3 is a graphical representation of a typical voltage-currentcharacteristic for electric discharge across a display cell;

FIG. 4 is an alternative illustrative embodiment of a display accordingto my invention;

FIG. 5 is another alternative illustrative embodiment of a displayaccording to my invention;

FIG. 6 is a block diagram of illustrative display arrangement 1showingportions of the control circuitry therefor in greater a detail;and

FIG. 7 is a time chartuseful in describing the operation of myinvention.

DETAILED DESCRIPTION In FIG. 1 of the drawing an illustrative plasmadisplay embodiment of the invention is shown comprising a stack ofconventional plasma display devices 101, l02'and 103, separated "byrespective light-attenuating layers 121 and 122, for

generating mural images by the selective energization of individual onesof the cross-point display cells of each device. Illustratively in FIG.I, the three display devices 101, 102 and 103 each comprise an 11x14coordinate array of I54 crosspoint display cells, the display cells ofeach device being substantiallyin registration with the correspondingdisplay cells of the other display devices in the stack. However, itwill be apparent from the description herein that the display cells maybe employed individually or in comlbinationin any form of array desiredfor particular display applications. For example, the display cells maybe arranged in'a spiral row or in concentric circles for radar displayapplications.

The cross-point display cells of each display device in FIG. 1 aredefmedby respective sets of rowand column conductors, such as row conductorsRll Rlll and column conductors 'C'lI-CIS of device 101, which are spacedapart by dielectric material layers,'such as layers 51 and 52.Dielectric material layers SI and 52, are in turn, spaced apart such asby spacers 55, and a substantially uniform continuous layer of gaseousdisplay material 53 is disposed between dielectric layers 51 and 52.Suitable gaseous display materials are well known in the art and maycomprise, for example, one or more of the inert gases or mixtures ofthese gases with other gases. Different gases, of course, have differentlightgspeed and color characteristics and the particular gaseous displaymaterial chosen will depend generally upon the application of thedisplay arrangement. Moreover, it will-be apparent that ditferentgaseous display materials may be employed in the various display devicelevels in the stack, or alternatively that appropriate filters may beemployed between the various levels, such as for multicolor displayapplications.

As is well known in the art, the dielectric mat'eriaL-such as layers 51and 52, may comprise plates of glass, plastic or other similartransparent material, each illustratively on the order of 5 mils or soin thickness and spaced apart a like distance by spacers 55. The row andcolumn conductors may comprise transparent metal or metal oxideconducting strips, for example, vapor-deposited on the respectivedielectric material layers. Illustratively, the row and columnconductors may be on the order of 15 mils wide and spaced apart on theorder of mils on the respective dielectric material layers.

A cross section of a portion of the display arrangement of FIG. 1 isdepicted in FIG. 2 showing, by way of example, the eight cross-pointdisplay cells of device 101 defined by column conductor C14 and rowconductors R12-R19. Similarly, the corresponding eight cells of device102 defined by column conductor C24 and row conductors R22-R29, and thecorresponding eight cells of device 103 defined by column conductor C34and row conductors R32-R39, are shown in FIG. 2.

Display devices 101, 102 and 103, in the illustrative embodiment of FIG.1, each utilize the mechanism of electrical discharge breakdown of thegaseous display material to the light-emitting plasma at selectedcross-point display cells for generating images. When an electric fieldis applied across a cross-point display cell, such as the cell definedby row conductor R12 and column conductor C14 of device 101, of abreakdown magnitude V determined by the pressure-distance characteristicof the particular gaseous display material employed, the gas in thecross-point region 220 breaks down and provides a light-emittingdischarge of low current density. A typical voltage-currentcharacteristic for such breakdown of a gas is shown in FIG. 3. As may beappreciated from FIG. 3, when voltage of increasing magnitude is appliedacross the display cell, very little current flows until the breakdownvoltage V is reached. At this point, the cell breaks down in a so-calledTownsend discharge characterized electrically by a substantiallyconstant low current density.

As the breakdown discharge and the resultant current flow areestablished initially at a cross-point display cell, charge is stored onthe surfaces of dielectric material layers 51 and 52 in the immediatevicinity of the cell cross-point. The stored charge opposes the voltagedrop across the display cell and quickly reaches a level where thevoltage across the cell becomes too low to maintain the discharge,thereby quenching the discharge at the cell.

In operation, an alternating current sustaining signal voltage providedby source 20, which may be either sinusoidal or pulsed, is extended bycontrol circuit 80 across each display cell of devices 101, 102 and 103via the row and column conductors. The sustaining signal voltageextended by source 20 across each display cell is of a magnitude lessthan the breakdown voltage level V,,. For example, the sustaining signalvoltage may be on the order of one-half the breakdown voltage level.

Addressing of a selected display cell of a particular display device inthe stack is effected via address circuit 30 under control of controlcircuit 80 by the application of coincident signals to the particularrow and column conductors defining the selected display cell. Thevoltage thus extended across the selected display cell by the coincidentrow and column signals, by itself or in conjunction with the sustainingsignal voltage applied to the row and column conductors, is sufficientto effect breakdown of the gaseous display material at the selectedcell. At the same time, however, the voltage extended across the otherdisplay cells connected to the addressed row and column conductors, isinsufficient to effect breakdown of the gas at these other cells.

As mentioned above, according to an important aspect of my invention,the individual display device levels in the stack are separated byrespective layers of light-attenuating material, such as layers 121 and122, which may be translucent glass or plastic, for example. Eachsuccessive light-attenuating layer in the stack attenuates the lightreaching the viewing surface by a predetermined amount, illustrativelyby a factor of two. Thus, the light reaching the viewing surface fromdisplay device 101 due to discharge at a cross-point display cellthereof is essentially unattenuated, while the light reaching theviewing surface from display device 102 due to discharge at a cell ofdevice 102 is attenuated one-half by light-attenuating layer 121.Similarly, the light emitted by discharge at a cell of display device103 is attenuated one-half by layer 122 and an additional one-half bylayer 121, such that the light finally reaching the viewing surface fromdevice 103 is attenuated by a factor of four.

It will be appreciated therefore, that at a selected crosspoint on theviewing surface of the embodiment of FIG. 1, the light presented to theviewer is controllable over a multilevel gray scale, having a range zeroto seven, by energization of the selected cross-point in variouscombinations of the display device levels. For example, the lightreaching the viewing surface at cross-point 5,4 in FIG; 2 due toenergization of devices 101, 102 and 103 at that cross-point would bethe maximum level attainable (e.g., a level of seven); while that atcrosspoint 8,4 due to energization of device 103 at that cross-pointwould be the next-to-lowest level (e.g., a level of one); and the lightat cross-point 2,4 due to energization of device 101 would be in themiddle of the range (e.g., a level offour).

Addressing of the individual cross-point display cells in FIG. 1 iseffected via conventional addressing or scanning techniques, such asthose known to the television art, advantageously employing a singleaddress circuit 30 in common for all the plasma display devices in thestack. As corresponding cross-point cells of devices 101, 102 and 103are addressed in common, the-cells of the respective devices areselectively energized at the addressed cross-point in accordance with agray scale input signal received by input circuit 50 from signal source10. The gray scale input signal from source 10 may be in analog form asis usual in commercial television, or preferably it may be in the formof a multibit digital word with respect bits of the word determining theON- OFF character of the individual display device cells at an addressedcross-point. If the signals from source 10 are received in analog form,control circuit must be provided with analog-to-digital encodingcircuitry to place the signals in digital form for energizing theindividual display cells of devices 101, 102 and 103.

Alternative display device arrangements are shown in FIGS. 4 and 5. Inthe embodiments of FIGS. 4 and 5, the row and column conductors, exceptfor the outermost sets of conductors, are each shared by two adjacentdisplay device levels. Thus, column conductors C42 are shared by displaydevices 401 and 402, and row conductors C43 are shared by devices 402and 403 in FIG. 4. An arrangement of n display devices therefore wouldrequire only n+1 sets of conductors interleaved with the display devicelevels, alternating between row conductors and column conductors asshown in FIG. 4. This arrangement advantageously facilitates manufactureby significantly reducing the number of sets of conductors and,consequently, the number of connections which must be made to thedisplay devices. Moreover, the embodiments of FIGS. 4 and 5 permitcloser spacing between display device levels in the stack than theembodiment of FIG. 1.

It will be appreciated that light-attenuating layer 421 may be disposedat any level in the stack intermediate the gaseous display material ofdevice 401 and the gaseous display material of device 402, and similarlythat light-attenuating layer 422 may be disposed at any level in thestack intermediate the gaseous display material of devices 402 and 403.Layer 421, for example, may comprise a light-attenuating film disposedon either surface of dielectric material layer 452 of device 401, or oneither surface of dielectric material layer 451 of device 402.

In the illustrative embodiment of FIG. 5, the row and column conductorsCSI-C54 comprise thin conductors coated or encased in dielectricmaterial such as glass or plastic. The sets of conductors are supportedand spaced apart by suitable spacers such as spacers 555 and adjacentdisplay device levels are separated by respective light-attenuatinglayers 521 and 522. Conductor CSIb-Cfid and light-attenuating layers 521and 622 are disposed in housing 630 having a transparent viewing surface53H, the housing being substantially filled with gaseous displaymaterial. Thus, conductors C51 and C62 in FIG. 5 comprise a firstdisplay device level corresponding to display device 401i in FIG. 4,conductors C52 and C63 comprise a second display device levelcorresponding to display device 462, and conductors C53 and C54 comprisea third display device level corresponding to device 4503. Theadvantages of the arrangement of FIG. 5 relative to facilitatingmanufacture are manifest. Moreover, unlike the embodiments of FIGS. land 43, the arrangement in FKG. 3 permits the individual conductors tobe removed and replaced, if required for repair or maintenance purposes.

With the above description in mind, and with reference to FIG. 6 and toFlGS. 7A, 7B and 7C, the operation of an illustrative displayarrangement according to my invention will now be considered. In FIG. 6a three-level display 666 is shown comprising plasma display devicelevels 6621, 662 and 603, which may be similar to the displayarrangement shown in FIG. t or H6. 6, for example. For the purposes ofdescribing the operation of the invention, only the three display cellsXa, Xb and X0 of a single cross-point of the display are depicted inFlG. 6. Assume initially that display cells Xa, Xb and Xc are OFF; i.e.,that no charge appears on the adjacent dielectric material surfaces andthat none of the three display cells are lighted. The sustaining signalvoltage from source 620 extended through OR gates 623 to row and columnconductors C6l-C64l defining cells Xa,Xb and X0 appears across eachdisplay cell, as shown in FlG. 7A. However, since the sustaining signalvoltage is less than the breakdown voltage V for the particular gaseousdisplay material employed, no significant current flow occurs throughthe display cells.

Each individual row and column conductor of display 666 is connected tothe output of a respective OR gate 623, one input of which, as justmentioned, is connected to source 626 and the other input of which isconnected to the output of a respective address gate associated with theindividual row or column conductor. A single address circuit 636 isemployed in common for all three plasma display levels in display 606,and is illustratively shown in FIG. 6 as providing an address signal ona respective one of leads 63l63m for each cross-point in the display.Thus each of leads 63l-63m is connected to an input of the four addressgates associated with the individual row and column conductors definingthe three display cells at a particular cross-point. The cross-pointcomprising display cells Xa, Xb and X0 is addressed, for example, by anaddress signal over lead 635 to one input of address gates 665, 666, 647and 668, gates 665 648 being individually associated with conductorsC6l-C6fil, respectively.

The other input of each address gate is connected to a respective one offour gray scale code leads Dl-Dd from address circuit 630. As eachcross-point is addressed, a gray scale input signal from signal source6% is registered as a three-bit word in input circuit 656, each bitdetermining the ON-OFF character of a respective cell at the addressedcrosspoint. The gray scale codeword bits are extended, one-at-atime, toaddress circuit 636 which responds to each bit to provide a signal oflike character on the corresponding pair of leads Dll-Dd. Thus,responsive to the first bit of a codeword from input circuit 650 addresscircuit 636 provides a gray scale signal of like character on code leadsD1 and D2, such as indicated by pulse 733 in FlG. 7C; responsive to thesecond bit, address circuit 630 provides a signal on code leads D2 andD3, such as indicated by pulse 732 in FIG. 7C; and responsive to thethird bit, a signal is provided on leads D3 and D41, such as indicatedby pulse 733.

Assume now that it is desired to turn ON display cells Xb and Xc definedby conductors C62 and C63 and by conductors C63 and C64 respectively.This is accomplished by addressing the selected display cross-point,extending a write pulse to display cell Xb in the form of coincidentsignals on conductors C62 and C63, and extending a write pulse todisplay cell X0 in the form of coincident signals on conductors C63 andC66. The write pulses extended to display cells Xb and Mo are ofsufficient potential to effect breakdown of the gaseous display materialat these cells.

Accordingly, with the illustrative example assumed, the gray scale wordOil is registered in input circuit 660 and extended, one-bit-at-a-time,to address circuit 630 during the interval that the cross-pointincluding cells Xa, Xb and Xc is addressed. No output appears on leadsDl-D4 responsive to the first bit from input circuit 650 since this bitis illustratively a binary zero. Responsive to the second bit,illustratively a binary one, address circuit 630 provides coincidentsignals on lead D2 and D3 to address gates 646 and 647. The signals onleads D2 and D3, in combination with the address signal on lead 635 asshown in FIG. 7B, enables gates 646 and 667 to provide a write pulseover leads C62 and C63 to display' cell Xb. This is shown as occurringat time I by way of example in FIG. 7A.

The write pulse applied to conductors C62 and C63 causes momentarybreakdown of the gaseous display material at dis play cell Xb,permitting current flow thereacross to store charge on the adjacentdielectric material surfaces. The resulting current flow across thedisplay cell during breakdown is in the form of a current pulse, shownas pulse 701 in FIG. 7C, which may illustratively have a duration on theorder of 50-75 nanoseconds.

Similarly, responsive to the third bit, illustratively a binary one,address circuit 630 provides coincident signals on leads D3 and D4 toaddress gates 6 37 and 648 which, in combination with the address signalon lead 635, provides a write pulse over leads C63 and C64 to displaycell Xc, at time !,in FIG. 7. Momentary breakdown of cell Xc occurs,permitting current flow thereacross, shown as pulse 702 in FIG. 7D, tostore charge on the adjacent dielectric material surfaces of cell Xc.

The level of charge stored .on the dielectric material surfaces isdetermined principally by the net voltage across the display cell duringbreakdown. During the following negative pulse of sustaining signalvoltage applied across the display cell, the stored charge adds to thesustaining signal voltage as shown in FIG. 7A. At time t the combinedvoltage exceeds the breakdown voltage V causing a momentary breakdowndischarge at display cells X12 and Xc. The resulting negative currentpulse 7'03, between conductors C62 and C63, removes the stored chargefrom the dielectric material surfaces adjacent cell Xb and charges thesurfaces in a reverse direction. Similarly, the negative current pulse704, between conductors C63 and C64, removes the stored charge from thedielectric material surfaces adjacent cell X0 and charges the surfacesin a reverse direction.

During the following positive pulse on. the sustaining signal voltage,therefore, the reverse charge on the dielectric material surfaces ofdisplay cells Xb and Xcadds to the sustaining signal voltage thereacrossas shown in Flg. 7A, reaching a level sufiicient to break down the gasat these display cells again at the time t During succeeding half-cyclesof the sustaining signal voltage, the charge stored on the dielectricmaterial surfaces of display cells Xb and X0, in combination with thesustaining signal voltage thereacross, causes periodic breakdown of thegas at these display cells to emit light in the form of pulseddischarges at a frequency twice that of sustaining signal source 620.

Additional ones of the display cells at other cross-points in display660 are turned ON in a similar manner by application of a write pulse tothe particular row and column conductors which define the additionalcells. Conversely, a selected display cell is turned OFF by applying anerase pulse to the row and column conductor defining the selected cell,such that the erase pulse substantially removes or erases the chargestored at the cell. This is effected, for example, by applying an erasepulse to the particular row and column conductors at a point betweensuccessive sustaining signal pulses, or at a point when theinstantaneous magnitude of the sustaining signal voltage applied to therow and column conductors is at or near zero in the case of a continuoussinusoidal sustaining signal.

Although in the description above it is tacitly assumed that only asingle display cell is addressed by a write or erase pulse during eachcycle of the sustaining signal voltage, it will be apparent that morethan one cell can be addressed during each sustaining signal voltagecycle by consecutively or concurrently addressing a number of cells ineach cycle. Further, the entire display can be erased if desired byterminating the sustaining signal voltage for a period sufficient topermit the stored charges at the display cells to dissipate. lt is to beunderstood, therefore, that the above described arrangements are butillustrative of the application of the principles of my invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

I claim:

1. In combination, a plurality of conductors, a plurality of gaseousdisplay cells, each of said display cells being defined by a pair ofsaid conductors separated by two layers of dielectric material having agaseous display material therebetween, means arranging said cells in astack, each cell comprising a respective level in said stack, and meansdisposed between said levels for attenuating light passing therethrough.

2. The combination in accordance with claim 1 wherein n display cellsare defined by n+1 conductors, said conductors being interleaved withsaid cells in said stack, and wherein n-l light attenuating means areinterleaved with said cells in said stack.

3. The combination in accordance with claim 2 further comprising aviewing surface, each of said light-attenuating means individuallyattenuating the intensity of light reaching said viewing surfacetherethrough by a factor of two.

4. The combination in accordance with claim l. further comprising meansfor selectively addressing individual ones of said display cells toinitiate a discharge breakdown thereat, and means connected to each ofsaid display cells and operative upon the initial discharge breakdown ofindividual ones of said cells for thereafter periodically breaking downsaid individual ones of said cells.

5. The combination in accordance with claim 4 wherein said addressingmeans comprises means for addressing selected ones of said display cellsin common, and means for selectively initiating said discharge breakdownat individual ones of said common addressed cells.

6. A display device comprising a plurality of gaseous display levels, aplurality of sets of conductors interleaved with said levels andarranged so as to define a respective array of display cross-points ateach of said levels, the display cross-points of each said array beingsubstantially in registration with corresponding display cross-points ofthe other ones of said arrays, and individual light-attenuating layersseparating adjacent ones of said display levels.

7. A display device according to claim 6 wherein each of said conductorscomprises an electrically conductive member separated from said gaseousdisplay levels by nonconductive material.

8. A display device according to claim 7 further comprising a housing,means stacking said sets of conductors in spacedapart relationship insaid housing, said display levels comprising a substantially uniformgaseous display material disposed in said housing between said stackedsets of conductors.

9. A display device according to claim 6 further comprising a viewingsurface, said light-attenuating layers each equally attenuating thelight reaching said viewing surface by passing therethrough.

M). A display device according to claim 9 wherein each light-attenuatinglayer attenuates the light reaching said viewing surface by a factor oftwo.

iii. A display device according to claim 6 further comprising means foraddressing corresponding cross-points at each of said display levels incommon, and means for initiating breakdown discharge at selected ones ofsaid common addressed cross-points.

12. A display device comprising a housing having a viewing surface,gaseous display material disposed throughout said housing, n+1 sets ofconductors, each conductor comprising an electrically conductive memberfrom said gaseous display material, means supporting said sets ofconductors in spacedapart relationship within said housing so as todefine a stack of n arrays of display cells, the cells of each arraybeing substantially in registration with corresponding cells of otherones of said arrays, and means disposed between adjacent ones of saidarrays for attenuating light passing therethrough by a predeterminedamount.

13. A display device according to claim 12 wherein said conductors eachcomprise an individual electrically conductive member coated withdielectric material, and wherein said conductors are supported by saidsupporting means so as to be individually removable from said housing.

M. A display device according to claim )12 wherein adjacent sets of saidconductors are disposed orthogonally so as to define individualcoordinate arrays in said stack.

RE. A plurality of conventional two state display cells, means arrangingsaid display cells in a stack, each cell in said stack beingsubstantially in registration with all other cells in said stack, andindividual light-attenuating means disposed between adjacent ones ofsaid display cells.

1. In combination, a plurality of conductorS, a plurality of gaseousdisplay cells, each of said display cells being defined by a pair ofsaid conductors separated by two layers of dielectric material having agaseous display material therebetween, means arranging said cells in astack, each cell comprising a respective level in said stack, and meansdisposed between said levels for attenuating light passing therethrough.2. The combination in accordance with claim 1 wherein n display cellsare defined by n1 conductors, said conductors being interleaved withsaid cells in said stack, and wherein n1 light attenuating means areinterleaved with said cells in said stack.
 3. The combination inaccordance with claim 2 further comprising a viewing surface, each saidlight-attenuating means individually attenuating the intensity of lightreaching said viewing surface therethrough by a factor of two.
 4. Thecombination in accordance with claim 1 further comprising means forselectively addressing individual ones of said display cells to initiatea discharge breakdown thereat, and means connected to each of saiddisplay cells and operative upon the initial discharge breakdown ofindividual ones of said cells for thereafter periodically breaking downsaid individual ones of said cells.
 5. The combination in accordancewith claim 4 wherein said addressing means comprises means foraddressing selected ones of said display cells in common, and means forselectively initiating said discharge breakdown at individual ones ofsaid common addressed cells.
 6. A display device comprising a pluralityof gaseous display levels, a plurality of sets of conductors interleavedwith said levels and arranged so as to define a respective array ofdisplay cross-points at each of said levels, the display cross-points ofeach said array being substantially in registration with correspondingdisplay cross-points of the other ones of said arrays, and individuallight-attenuating layers separating adjacent ones of said displaylevels.
 7. A display device according to claim 6 wherein each of saidconductors comprises an electrically conductive member separated fromsaid gaseous display levels by nonconductive material.
 8. A displaydevice according to claim 7 further comprising a housing, means stackingsaid sets of conductors in spaced-apart relationship in said housing,said display levels comprising a substantially uniform gaseous displaymaterial disposed in said housing between said stacked sets ofconductors.
 9. A display device according to claim 6 further comprisinga viewing surface, said light-attenuating layers each equallyattenuating the light reaching said viewing surface by passingtherethrough.
 10. A display device according to claim 9 wherein eachlight-attenuating layer attenuates the light reaching said viewingsurface by a factor of two.
 11. A display device according to claim 6further comprising means for addressing corresponding cross-points ateach of said display levels in common, and means for initiatingbreakdown discharge at selected ones of said common addressedcross-points.
 12. A display device comprising a housing having a viewingsurface, gaseous display material disposed throughout said housing, n1sets of conductors, each conductor comprising an electrically conductivemember and dielectric material separating said conductive member fromsaid gaseous display material, means supporting said sets of conductorsin spaced-apart relationship within said housing so as to define a stackof n arrays of display cells, the cells of each array beingsubstantially in registration with corresponding cells of other ones ofsaid arrays, and means disposed between adjacent ones of said arrays forattenuating light passing therethrough by a predetermined amount.
 13. Adisplay device according to claim 12 wherein said conductors eachcomprise an individual electrically conductive member coated withdielectric material, and wherein said conductors are Supported by saidsupporting means so as to be individually removable from said housing.14. A display device according to claim 12 wherein adjacent sets of saidconductors are disposed orthogonally so as to define individualcoordinate arrays in said stack.
 15. A plurality of conventional twostate display cells, means arranging said display cells in a stack, eachcell in said stack being substantially in registration with all othercells in said stack, and individual light-attenuating means disposedbetween adjacent ones of said display cells.